1. Field of the invention
The present invention relates to an image forming device, an ink sheet cartridge for use in the image forming device, and an exchangeable ink-sheet set available for the ink sheet cartridge.
2. Related Art
Usually, a thermal printer uses an ink ribbon cartridge for printing an image on a recording sheet in terms of ease of exchange and handling. When the thermal printer is a line printer, an ink ribbon cartridge including a wide ink sheet is used. As disclosed in Japanese Utility Model Application Publication No. HEI-6-81749 and Japanese Patent Application Publication No. HEI-10-193732, this type of conventional ink sheet cartridges include a cartridge body, a supply-side member, a takeup-side member, and an ink sheet wound around the supply-side and takeup-side members. The supply-side and takeup-side members are rotatably supported on the cartridge body and detached from the cartridge body when replacing the ink sheet.
The cartridge body includes a pair of covering portions for covering over the upper and lower sides of the outer peripheral surfaces of the supply-side and takeup-side members. The covering portions have a semi-circular cross-sectional shape. Also, the cartridge body is formed in a frame-like shape so as to define a center space where the ink sheet is exposed. Providing the covering portions to the cartridge body increases rigidity of the cartridge body. However, this arrangement increases production cost.
According to Japanese Patent Application Publication No. HEI-10-193732, when the above-described ink sheet cartridge is accommodated in the image forming device, a thermal head provided to the image forming device is positioned below the center space so as to slidingly contact the lower surface of the ink sheet exposed therefrom. On the other hand, a recording sheet is brought into contact with the upper surface of the exposed portion of the ink sheet. After printing is performed on the recording sheet by the thermal head, the recording sheet is transported along a U-shaped sheet passage extending upwardly. This configuration requires a transport chute at the main body or a cover of the image forming device for separating the recording sheet from the ink sheet, and the attachment position of the transport chute is severely restricted to prevent the transport chute from being an obstacle against exchange of the ink sheet cartridge.
On the other hand, according to Japanese Utility Model Application Publication No. HEI-6-81749, the thermal head is provided in sliding contact with the upper surface of the ink sheet, and the recording sheet is transported into abutment with the lower surface of the ink sheet. After printing is performed, the recording sheet is discharged out of the image forming device at a position below the ink sheet cartridge. A front side of the main body case is provided with a door, through which the ink sheet cartridge is inserted into the main body case. Also, a sheet cassette for accommodating the recording sheets is provided next to a side of the main body case close to the door at a position lower than the ink sheet cartridge. The sheet cassette is detachable from the front portion of the main body case.
However, with this configuration, an additional working space is required in front of the main body case for exchanging the recording sheets and the ink sheet cartridge. Because a space for disposing a control board, which controls operation of the image forming device, is also required in the main body case, the main body case has undesirably a large size. Moreover, when recording sheet jamming occurs, the ink sheet cartridge must be removed from the main body case in order to remove the jammed recording sheet from the lower side of the ink sheet cartridge.
Incidentally, each of the supply-side member and the takeup-side member has a core tube for winding thereon the ink sheet and a pair of spools attached to right and left ends of the core tube. One of the pair of spools is provided with a gear. When assembling the ink sheet cartridge into the image forming device, first the spools are engaged with the corresponding ends of the core tubes, and the core tubes are mounted on the cartridge body case via the spools. Then, the ink sheet cartridge is mounted to the main body of the image forming device such that the gears of the spools are meshed with corresponding gears provided to the main body case. With this configuration, the driving power is transmitted from the main body of the image forming device to the spools via the gears, thereby rotating the core tubes for feeding the ink sheet.
However, there has been a danger that a user may erroneously attach the supply-side and takeup-side members on the cartridge body. For example, the left and the right of the members may be opposite. If the members are erroneously attached to the cartridge body, upper and lower surfaces of an ink sheet will be reversed, so that printing operation becomes inoperative. Also, if the gear is set at erroneous side of the cartridge body, supply of the ink sheet becomes impossible. However, attachment work for attaching the members and spools at correct positions and orientations is bothering and troublesome for a user.
Moreover, an ink sheet having an ink quality different from a regular ink sheet, such as those of different manufacturer, may be accidentally used. When an ink sheet having a width, a dimension, a sheet material, and an ink material different from those of a regular ink sheet is incorporated into the ink sheet cartridge and used in the image forming device, normal printing will be prevented. This will undesirably degrade a quality of recorded images, which should have an excellent image quality otherwise.
The conventional image forming device is also provided with a torque limiter at the power transmission portion of the main body case. The torque limiter enables taking up of the ink sheet with a proper tension, and also prevents excessive tension from being applied to the ink sheet by providing slippage at the power transmitting region when a torque value is exceeded a maximum torque value so as to is reduce power transmission from the main body to the takeup-side member.
The maximum torque value required for taking-up the ink sheet differs in accordance with a thickness, a width, and a material of the ink sheet. However, because the torque limiter is provided to the main body case of the image forming device, it is difficult and troublesome to change the maximum torque value each time and every time a different ink sheet is used.
There has been also provided a torque transmission mechanism where one end of each core tube is formed with a notched groove open to the one end, and one of the pair of spools is provided with an engagement projection engageable with the notched groove. With this configuration, torque is transmitted to the core tubes for taking up the ink sheet with a proper tension, and the torque limiter provided to the main body case of the image forming device can be dispensed with.
However, because the maximum torque value differs in accordance with the ink sheet as described above, a dimension of inner and outer diameters of the core tube where the ink sheet is wound around also differs. Accordingly, each time when a different type of ink sheet is used, spools having a corresponding diameter are needed. This causes increase in production cost.